Acetabular prostheses are known for use as a component for a total hip prosthesis. Acetabular prostheses typically include two separate components, one of which is a cup or shell that is affixed within a cavity reamed in healthy bone of the acetabulum. The acetabular cup may have an external (i.e., bone-contacting) geometry that is appropriate for a given patient. The inner geometry of the acetabular cup is usually characterized by a smooth, generally spherical cavity. The acetabular cup is typically made of a metal or metal alloy. In some cases, however, polymeric acetabular cups are utilized.
A liner component is often mated with the inner geometry of the acetabular cup to provide a low friction bearing surface that articulates with a femoral head. The liner may have an outer, spherical surface that is of a size and shape to enable it to mate with the inner surface of the acetabular cup. The inner surface of the liner likewise is hemispherically shaped, having a smooth, low friction surface. As noted above, the femoral head seats within and articulates with the internal surface of the liner.
Acetabular cups are often made from a metal or metal alloy. Some designs, however, utilize polymeric cups. One polymer commonly used to form the liner is ultrahigh molecular weight polyethylene. However, it is also possible to fabricate the liner from other materials, including metals, metal alloys and ceramics.
Regardless of the materials and geometries used for the acetabular prosthesis, the acetabular cup and liner must be joined together, usually during the course of a surgical procedure. That is, a surgeon first implants the acetabular cup within the patient's acetabulum. Thereafter, the liner is separately affixed within the acetabular cup. A variety of liner designs exist and many are not symmetrical. Thus, the surgeon must determine the appropriate orientation of the liner with respect to the cup. Once the liner is properly oriented, it must remain so after affixation within the cup.
Some acetabular prosthesis designs do not permit easy mating of the liner to the cup; the mating of some designs can, in fact, be quite challenging. Specialized tools or separate components may be necessary to join these components or to permanently affix them together. In some instances the locking mechanism must be assembled during the surgical procedure. Such additional steps may render the attachment process more time-consuming and may introduce the possibility that the liner and the shell will become misaligned due to surgical technique or for other reasons. Further, there is always a possibility that the joinder mechanism may fail to achieve its objective to secure the two components to one another.
A number of patents describe acetabular prostheses designs that utilize a separate component to lock the liner and the shell together. Examples of such patents include U.S. Pat. Nos. 4,619,658; 4,770,658; 4,784,663; 4,969,910; 5,049,158; 5,171,285; 5,263,988; 5,425,779; 5,507,826; and 5,658,348.
Other known designs do not require a separate locking mechanism to join the liner and the cup. Instead, an interference fit or another form of mechanical engagement of the two components is relied upon. Examples of patents disclosing such attachment mechanisms include U.S. Pat. Nos. 4,172,296; 4,650,491; 5,376,122; 5,443,519; and 5,549,698.
Despite the acetabular prostheses designs that are known to exist, there is still a need for an acetabular prosthesis design that provides excellent attachment strength between the liner and the cup while at the same time providing ease of assembly without the need for additional assembly tools or components.